Thursday, July 06, 2006

Debbie Argue and colleagues have a new paper in press in the Journal of Human Evolution about the Liang Bua 1 specimen that, well, argues that LB1 does, in fact, represent a specimen of a distinct species rather than either a microcephalic or 'pygmoid' Homo sapiens individual. Their case is based on an evaluation of the physical characteristics of documented cases of various forms of microcephaly and dwarfism, as well as those of pygmoid individuals in the literature, including one from Flores. They conclude that beyond a small cranial capacity, the LB1 specimen shares almost nothing in common morphologically with microcephalic humans. Overall, their argument is well structured and relatively expansive, covering as it does both cranial and postcranial characteristics, and including a wide range of comparative datasets, although some of them (especially the microcephalic modern humans, with only two specimens) are pretty sparse quantitatively. As they state themselves, “Microcephaly is an extremely heterogeneous condition and, while our results are suggestive, it may be that they would differ should a larger sample of microcephalics be studied” (Argue et al. 2006: ms. p. 20). I'm sure defenders of the alternative positions about the specific status of the Liang Bua remains will promptly have more to say about these data and the resulting analysis, however, so keep posted.

To me, however, perhaps the most interesting aspect of the paper is the scenario about the evolutionary history of H. floresiensis, since Argue et al. don't believe that it descended from Asian H. erectus, which had been held as a potential ancestor for H. floresiensis. Rather, they propose a number of alternative evolutionary scenarios which mention as a possible ancestor an Australopithecine-like or unknown early Homo species that would have diffused out of Africa by ca. 2 mya. As the authors themselves acknowledge, however, there remains to explain just how that ancestral population would have reached Flores and subsequently become genetically isolated. The idea, which Argue et al. mention, that they might have “washed ashore” strikes me as very unlikely. There would have been a need for a population of those critters to be flung there by the seas in order for it to be genetically viable, which is hardly a likely scenario in my opinion. Importantly, they also raise the question of why hominins stuck on Flores should have necessarily become dwarfed, since the island hardly qualifies as a “predator-free environment,” at least for hominins. This, however, also raises the question of why Stegodon should have become dwarfed if they were predated by technologically-able hominins like LB1 who might have been on the island for almost two million years.

From a purely archaeological perspective, this paper raises some interesting issues, too. First, it implies that whoever settled on Flores had some kind of seafaring ability, no matter how rudimentary. Conversely, it implies that modern humans, who were almost certainly in the area by about 60kya and had seafaring capacities, did not for some reason settle Flores for almost 50,000 years! Given the short thrift most archaeologists seem to think modern humans gave the Neanderthals, (and who occupied almost the whole of Eurasia!), it seems unlikely that the “fearsome local” scenario would make much sense for Flores, especially since modern human hunter-gatherers were on the island by ca. 10Kya anyway, with much the same technology as modern hunter-gatherers of the region had by 60kya. Secondly, if Flores was reached ca. 2 mya by the direct ancestors of the Linag Bua specimens, it implies that there should be a complete Oldowan-to-blade-technology technological strategy (or something similar) documented in the archaeological record of the island. The recent paper by Brumm et al. (2006) certainly provides evidence for one potential point along that continuum (although their case for any “technological continuity” on Flores between 800-12 kya certainly is far from solid – I intend to post more on this later), but one would expect both older and, so to speak, coarser lithic technological strategies to be documented on the island. These concerns, of course, presuppose that Argue and colleagues are right, something which only time will tell. However, as in all paleoanthropology, these questions demonstrate that it is imperative, when formulating evolutionary scenarios, to integrate all facets of prehistoric hominin life, both morphological and archaeological. As it is, until we also get data that would enable a discussion of those archaeological questions, there is still a lot to be done in order to demonstrate that Homo floresiensis is indeed a separate species.